Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764470AbZDBRly (ORCPT ); Thu, 2 Apr 2009 13:41:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755363AbZDBRlo (ORCPT ); Thu, 2 Apr 2009 13:41:44 -0400 Received: from mail-gx0-f160.google.com ([209.85.217.160]:49334 "EHLO mail-gx0-f160.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755558AbZDBRln (ORCPT ); Thu, 2 Apr 2009 13:41:43 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:in-reply-to:references:date:subject:from:to:cc :user-agent:mime-version:content-type:content-transfer-encoding :x-priority:importance; b=PI8OAPQA9dikQRW5Hu3sK4GxVdQC2NWkPvqJojjfkOByMz643VjujzI5vt1cNyphkw DhNDULY3fHI2w2ShgQLSBBMP5zXif+64JrqiTzzCMjJbElrNmSuoXvE/Wyfz0ovDUg1M 64rjQh//1qJqCLBsfbdEht5//x2rt1PeS3cgU= Message-ID: <6c62e9d84a16902aebba9438b4e299d9.squirrel@localhost> In-Reply-To: <159a870e0904020702q3c528b8u77cebf834d607e3f@mail.gmail.com> References: <159a870e0904020702q3c528b8u77cebf834d607e3f@mail.gmail.com> Date: Thu, 2 Apr 2009 12:41:37 -0500 (CDT) Subject: Re: RAID performance / tuning? From: david.hagood@gmail.com To: "Tiago Freire" Cc: linux-kernel@vger.kernel.org User-Agent: SquirrelMail/1.4.15 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1020 Lines: 26 > Why is it that software RAID on current systems still gets less > performance than hardware counterparts? Part of it can be crappy disk interfaces: I was running software raid with 2 SATA-SIL cards, and would frequently be disk-bound with the CPU still largely idle. The cards were incapable of talking to more than one drive at a time. They didn't support command queuing on the drives. As a result, the system would set up a stripe, queue up the writes, then have to wait as each write for EACH DISK in the 7 disk array was carried out. On a good hardware RAID controller, the disks can be written in parallel, and the controller will support command queuing - so disk writes can be run in parallel, and the writes themselves can be better optimized by the disks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/